System for efficient cold energy power generation through organic Rankine cycle and power generation method thereof

Abstract

The invention belongs to the field of direct utilization of liquefied natural gas cold energy, and particularly relates to a system for efficient cold energy power generation through organic Rankine cycle and a power generation method of the system. The system for efficient cold energy power generation through the organic Rankine cycle comprises a main heat exchanger, a Rankine cycle refrigerant booster pump, an NG thermolator, a first heat exchanger, a second heat exchanger, a third heat exchanger, a first Rankine cycle turbine, a second Rankine cycle turbine, a second Rankine cycle turbine and a power generator. The invention provides a novel cyclic power generation method by combining the characteristics that LNG receiving stations in China are mostly used for peak regulation stations and the working pressure is high. According to the method, a mixed working medium is selected as a refrigerant, seawater or other industrial waste heat is used as a high-temperature section heat source, organic Rankine cycle is used for doing work outwards, three-section power generation comprehensively recovers cold energy released during LNG gasification, and 42 kWh of power is generated for each ton of LNG according to the system and the power generation method through calculation.

Description

Technical Field

[0001] The present invention belongs to the field of direct utilization of liquefied natural gas cold energy, and specifically relates to a system and a power generation method thereof for high-efficiency cold energy power generation using an organic Rankine cycle. Background Art

[0002] Liquefied Natural Gas (LNG) is transported and stored at -162℃. Before use, the low-temperature LNG needs to be gasified into natural gas (NG) at room temperature. The gasification process releases about 830kJ / kg of cold energy. At present, my country's large-scale LNG receiving stations all use open rack seawater vaporizers (ORV) to use seawater as a heat source to gasify LNG. The harm caused by the release of a large amount of cold energy in the LNG gasification process to the surrounding marine ecological environment has attracted social attention. At the same time, natural gas, as a relay energy for achieving my country's dual carbon goals of "carbon peak and carbon neutrality", has an irreplaceable position in the next few decades. my country's natural gas demand has maintained a growth momentum. At present, the domestic self-produced gas and imported pipeline gas supply cannot meet downstream demand, and can only significantly increase LNG spot imports. In 2021, my country's LNG imports will be about 78.93 million tons. Based on 50% LNG cold energy recovery and utilization, my country's LNG cold energy available in 2021 will be about 8 billion kWh. If the cold energy of LNG is effectively recovered, it can achieve energy conservation and environmental protection, and at the same time obtain good economic and social benefits.

[0003] Cold energy power generation is a way to directly utilize LNG cold energy. The electricity generated by this method can be directly used by receiving stations or surrounding enterprises. Compared with other cold energy utilization methods, it has no restrictions on raw materials and no product sales pressure. It is an economical, efficient and environmentally friendly energy recovery method. Large LNG receiving stations have huge cold capacity, and different power generation plans should be formulated according to the purpose of LNG. LNG used as long-distance pipeline fuel has a high gasification pressure, and the low-temperature Rankine cycle can be used to recover cold energy during the LNG gasification stage. , recover pressure when regulating pressure at urban pressure regulating station The gasification pressure for direct power generation in power plants is relatively low, and the combined method can be used to recover the cooling capacity at the gasification stage. and pressure At present, my country's LNG receiving stations are mostly used as peak-shaving stations for urban gas, with a gasification pressure of 6 to 10 MPa and high working pressure. It is necessary to seek a more suitable cold energy power generation method to efficiently recover LNG cold energy.

[0004] A Chinese invention patent (application number 201210445501.1) discloses a method for cascading the use of liquefied natural gas cold energy for power generation, which includes two parts: a natural gas medium Rankine cycle and a refrigerant medium Rankine cycle. The natural gas medium Rankine cycle includes steps such as the natural gas medium absorbing cold energy to liquefy and expand to do work. A Chinese invention patent (application number 202011567411.0) discloses a cold energy power generation method combining an organic Rankine cycle and a Brayton cycle. This method uses the flue gas at the outlet of the gas turbine as a heat source for the supercritical CO2 recompression Brayton cycle, realizes the efficient complementary utilization of BOG and LNG cold energy, and improves the thermal efficiency and power generation efficiency of the power generation system. A Chinese invention patent (application number 202022482601.4) discloses a cold energy power generation method including an auxiliary heating unit. This method heats the reheating medium through the auxiliary heating unit, which compensates for the influence of the low temperature of the reheating medium on the reheating effect in winter. This method reduces the influence of some environmental factors on the power generation system. Summary of the invention

[0005] The purpose of the present invention is to provide a system and a power generation method for efficient cold energy generation using an organic Rankine cycle in combination with the working characteristics of my country's receiving stations. The main working principle of the present invention is that a low-temperature working fluid performs work externally through a Rankine cycle. Compared with the common high-temperature steam Rankine cycle, the present invention uses LNG as the low-temperature end of the Rankine cycle and seawater as the high-temperature end of the Rankine cycle. The power generation system described in the present invention uses an organic Rankine cycle to perform work externally, and the three-stage power generation comprehensively recovers the cold energy released during LNG gasification. It has been calculated that the system and method described in the present invention generates 42kWh of electricity per ton of LNG.

[0006] The implementation process of the present invention is as follows:

[0007] A system for high-efficiency cold energy power generation using an organic Rankine cycle comprises a main heat exchanger, a Rankine cycle refrigerant booster pump, an NG thermostat, a No. ① heat exchanger, a No. ② heat exchanger, a No. ③ heat exchanger, a No. ① Rankine cycle turbine, a No. ② Rankine cycle turbine, a No. ② Rankine cycle turbine and a generator; LNG from a receiving station is connected to a first channel of the main heat exchanger through a pipeline, the first channel of the main heat exchanger is connected to the NG thermostat, LNG is gasified into gas in the main heat exchanger, and is temperature-regulated by the thermostat before entering a pipeline network and being transported to users; the No. ③ Rankine cycle turbine is connected to a first channel of the main heat exchanger through a pipeline, the first channel of the main heat exchanger is connected to the NG thermostat, the LNG is gasified into gas in the main heat exchanger, and is temperature-regulated by the thermostat before entering a pipeline network and being transported to users; the No. ③ Rankine cycle turbine is connected to a first channel of the main heat exchanger through a pipeline, the first channel of the main heat exchanger is connected to the NG thermostat, the LNG is gasified into gas in the main heat exchanger, the gas is temperature-regulated by the thermostat ... The second channel of the main heat exchanger is connected to the refrigerant booster pump through a refrigerant pipeline, the refrigerant booster pump is connected to the third channel of the main heat exchanger through a refrigerant pipeline, the third channel of the main heat exchanger is connected to heat exchanger No. ① through a refrigerant pipeline, heat exchanger No. ① is connected to turbine No. ① through a refrigerant pipeline, turbine No. ① is connected to heat exchanger No. ② through a refrigerant pipeline, heat exchanger No. ② is connected to turbine No. ③ through a refrigerant pipeline, turbine No. ①, turbine No. ② and turbine No. ③ work to drive the coaxial generator to generate electricity.

[0008] Furthermore, the main heat exchanger adopts a multi-channel high-pressure plate-fin heat exchanger, which can realize efficient heat exchange of multiple logistics at the same time; the refrigerant booster pump adopts a submersible pump.

[0009] Furthermore, the heat exchangers No. ①, No. ② and No. ③ all adopt open-frame vaporizers.

[0010] Furthermore, the turbine No. 1, turbine No. 2 and turbine No. 3 are all coaxial centrifugal turbine expanders.

[0011] Furthermore, the generator is a synchronous generator, which is coaxial with turbine No. 1, turbine No. 2 and turbine No. 3.

[0012] Furthermore, the refrigerant of the power generation system is a mixed working fluid consisting of methane, ethylene and propane.

[0013] The power generation method of the system using the organic Rankine cycle for high-efficiency cold energy power generation comprises the following steps:

[0014] (1) LNG stored at normal pressure and low temperature is pressurized by a high-pressure pump. The pressurized LNG enters the first channel of the main heat exchanger through a pipeline, and exchanges heat with the gaseous refrigerant in the second channel of the main heat exchanger in the main heat exchanger. The LNG after heat exchange is converted into NG, and enters the NG thermostat through a pipeline, where it is reheated to above 0°C and then enters the pipeline network for transmission to users.

[0015] (2) The gaseous refrigerant exchanges heat with the LNG in the first channel in the second channel of the main heat exchanger and condenses into liquid refrigerant;

[0016] (3) The liquid refrigerant enters the refrigerant booster pump through the pipeline for pressurization. The liquid refrigerant with increased pressure enters the third channel of the main heat exchanger, exchanges heat with the gaseous refrigerant in the second channel of the main heat exchanger, and a small amount of refrigerant is vaporized;

[0017] (4) After completing step (3), the refrigerant enters heat exchanger No. ① through the pipeline for heat exchange. In this step, the refrigerant is completely vaporized and the temperature rises;

[0018] (5) The heated gaseous refrigerant enters turbine No. 1 through the pipeline to perform the first expansion and work. After the work, the temperature of the gaseous refrigerant decreases;

[0019] (6) After the first expansion, the gaseous refrigerant enters heat exchanger No. ② through the pipeline for heat exchange and reheating;

[0020] (7) The reheated gaseous refrigerant enters turbine No. ② through the pipeline to expand and perform work for the second time;

[0021] (8) After the second expansion, the gaseous refrigerant enters heat exchanger No. ③ through the pipeline for heat exchange and reheating;

[0022] (9) The reheated gaseous refrigerant enters turbine No. 3 through the pipeline to expand for the third time and perform work;

[0023] (10) After the third expansion, the gaseous refrigerant enters the second channel of the main heat exchanger through the pipeline, forming a refrigerant circulation process;

[0024] (11) Turbine No. 1, Turbine No. 2 and Turbine No. 3 output power to drive the coaxial generator to generate electricity, thereby converting the cold energy of LNG into electrical energy. The electrical energy generated by the generator can be connected to the electrical bus of the receiving station for use by the receiving station.

[0025] Furthermore, in step (1), the high-stage heat source may be seawater or an immersion combustion gasifier. In steps (4), (6), and (8), the high-stage heat source may be seawater as the high-temperature stage heat source of the low-temperature Rankine cycle, or industrial waste heat such as hot wastewater, waste steam, or an immersion combustion gasifier may be used as the high-stage heat source to improve the power generation efficiency of the system.

[0026] Furthermore, the pressure of the liquid refrigerant after the pressure increase in step (3) is 22 bar; the pressure of the gaseous refrigerant after the first expansion work is 16 bar; the pressure of the gaseous refrigerant after the second expansion work is 10 bar, and the pressure of the gaseous refrigerant after the third expansion work is 4 bar.

[0027] Furthermore, the gaseous refrigerant or liquid refrigerant is a mixed working fluid consisting of methane, ethylene and propane, with molar percentages of 32%, 28% and 40% respectively.

[0028] Positive effects of the present invention:

[0029] (1) The system and method of the present invention selects a mixed working fluid composed of methane, ethylene and propane as a cold energy refrigerant. The working curve of the mixed working fluid is basically consistent with the gasification curve of LNG, thereby improving the cold recovery efficiency.

[0030] (2) The system and method described in the present invention use seawater as the heat source for the high temperature stage of the low temperature Rankine cycle. Industrial waste heat such as hot wastewater, waste steam, or an immersed combustion gasifier may be used as a high stage heat source to improve the power generation and efficiency of the system.

[0031] (3) The system and method of the present invention adopts a low-temperature organic Rankine cycle three-stage power generation, and a reheating process is set in the middle to improve the power generation efficiency of the system. The three-stage power generation adopts a coaxial centrifugal turbine expander to drive a coaxial generator to generate electricity, and the generator adopts a synchronous generator.

[0032] (4) The main heat exchanger of the system and method described in the present invention adopts a multi-channel high-pressure plate-fin heat exchanger, which can realize efficient heat exchange of multiple logistics at the same time; the natural gas heat exchanger and the refrigerant heat exchanger adopt the open-frame gasifier commonly used in large LNG receiving stations, and the refrigerant booster pump adopts a submersible pump.

[0033] (5) The system and method of the present invention, combined with the characteristics of LNG gasification in my country, are suitable for cold energy power generation at large LNG receiving stations in my country at this stage. According to calculations, the system and method of the present invention can generate 42 kWh of electricity per ton of LNG.

[0034] (6) The system and method of the present invention have simple process flow and high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a system flow chart of the present invention using the organic Rankine cycle for efficient cold energy generation;

[0036] Among them, H001-main heat exchanger; H201-NG thermostat; P101-Rankine cycle refrigerant booster pump; H101-heat exchanger No. ①; H102-heat exchanger No. ②; H103-heat exchanger No. ③; T101-Rankine cycle turbine No. ①; T102-Rankine cycle turbine No. ②; T103-Rankine cycle turbine No. ③; W101-generator. DETAILED DESCRIPTION

[0037] The method of the present invention is described below by means of specific examples, but the present invention is not limited thereto.

[0038] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0039] Example 1

[0040] A system for high-efficiency cold energy generation using an organic Rankine cycle, see Figure 1, including main heat exchanger H001, NG thermostat H201, Rankine cycle refrigerant booster pump P101, heat exchanger No. ① H101, heat exchanger No. ② H102, heat exchanger No. ③ H103, Rankine cycle turbine No. ① T101, Rankine cycle turbine No. ② T102, Rankine cycle turbine No. ③ T103 and generator W101; the LNG pipeline from the receiving station is connected to the first channel of the main heat exchanger H001, the first channel of the main heat exchanger H001 is connected to the thermostat H201 through a pipeline, LNG is gasified into gas in the main heat exchanger, and is temperature-regulated by the thermostat and then transported to users outside the pipeline network; No. ③ Rankine cycle turbine T103 is connected to the second channel of the main heat exchanger H101 through a pipeline, the main heat exchanger H001 The second channel of the Rankine cycle refrigerant booster pump P101 is connected through a refrigerant pipeline, the Rankine cycle refrigerant booster pump P101 is connected to the third channel of the main heat exchanger H001 through a refrigerant pipeline, the third channel of the main heat exchanger H001 is connected to the No. ① heat exchanger H101 through a refrigerant pipeline, the No. ① heat exchanger H101 is connected to the No. ① Rankine cycle turbine T101 through a refrigerant pipeline, the No. ① Rankine cycle turbine T102 is connected to the No. ② heat exchanger H102 through a refrigerant pipeline, the No. ② heat exchanger H203 is connected to the No. ③ Rankine cycle turbine T103 through a refrigerant pipeline, the No. ① Rankine cycle turbine T101, the No. ② Rankine cycle turbine T102, and the No. ③ Rankine cycle turbine T103 work to drive the generator W101 to generate electricity. The electricity generated by the system can be directly used by the receiving station or surrounding enterprises.

[0041] Among them, the main heat exchanger H001 adopts a high-pressure plate-fin heat exchanger; the Rankine cycle refrigerant booster pump P101 adopts a submersible pump. The heat exchanger No. 1 H101, the heat exchanger No. 2 H102, the heat exchanger No. 3 H103, and the NG thermostat H201 all adopt open-frame vaporizers. The Rankine cycle turbine No. 1 T101, the Rankine cycle turbine No. 2 T102, and the Rankine cycle turbine No. 3 T103 all adopt centripetal turbine expanders. The generator W101 adopts a synchronous coaxial generator. The refrigerant of the power generation system uses a mixed working fluid composed of methane, ethylene, and propane.

[0042] The power generation method of the system using the organic Rankine cycle for high-efficiency cold energy power generation comprises the following steps:

[0043] (1) LNG stored at normal pressure and low temperature is pressurized by a high-pressure pump. The pressure after pressurization is 80 bar, the temperature is -150°C, and the flow rate is 100 t / h. The pressurized LNG enters the first channel of the main heat exchanger H001 through a pipeline, and exchanges heat with the gaseous refrigerant in the second channel of the main heat exchanger H101 with a flow rate of 95.5 t / h, a temperature of -15.5°C, and a pressure of 4 bar, transferring cold energy to the gaseous refrigerant. The LNG after heat exchange is converted into NG, and enters the NG thermostat H201 through a pipeline, where it is reheated to above 0°C and enters the pipeline network for transmission to users.

[0044] (2) The gaseous refrigerant is cooled to -145°C in the second channel of the main heat exchanger H101 by heat exchange with the LNG in the first channel, and condenses into liquid refrigerant;

[0045] (3) The liquid refrigerant enters the Rankine cycle refrigerant booster pump P101 through a pipeline and is pressurized to 22 bar. The liquid refrigerant with increased pressure enters the third channel of the main heat exchanger H001 and exchanges heat with the gaseous refrigerant in the second channel of the main heat exchanger H101, and a small amount of refrigerant is vaporized;

[0046] (4) After completing step (3), the refrigerant enters heat exchanger H102 through the pipeline for heat exchange. In this step, the refrigerant is completely vaporized and the temperature rises to 15°C;

[0047] (5) The reheated gaseous refrigerant enters the No. 1 Rankine cycle turbine T101 through a pipeline for the first expansion to perform work to 16 bar. After the work is performed, the temperature of the gaseous refrigerant drops to -15.5°C;

[0048] (6) After the first expansion, the gaseous refrigerant enters heat exchanger H102 through the pipeline to exchange heat and reheat to 15°C;

[0049] (7) The reheated gaseous refrigerant enters the Rankine cycle turbine T102 through the pipeline for the second expansion to perform work to 10 bar. After the work is performed, the temperature of the gaseous refrigerant drops to -15.5°C;

[0050] (8) After the second expansion, the gaseous refrigerant enters heat exchanger H103 through the pipeline to exchange heat and recover the temperature to 15°C;

[0051] (9) The reheated gaseous refrigerant enters the No. 3 Rankine cycle turbine T103 through a pipeline for the third expansion to perform work to 4 bar. After the work, the temperature of the gaseous refrigerant drops to -15.5 bar;

[0052] (10) After the third expansion, the gaseous refrigerant enters the second channel of the main heat exchanger H101 through the pipeline, forming a refrigerant circulation process;

[0053] (11) The high-stage heat sources H101, H102, and H103 use seawater as the high-temperature stage heat source of the low-temperature Rankine cycle. Industrial waste heat such as hot wastewater, waste steam, or an immersed combustion gasifier can also be used as the high-stage heat source to improve the power generation efficiency of the system. The flow rate of the high-temperature stage heat source seawater is automatically adjusted by the control system according to the refrigerant outlet temperature.

[0054] (12) Rankine cycle turbines T101, T102 and T103 output power to drive generator W101 to generate electricity, thus converting LNG cold energy into electrical energy. According to simulation calculations, the above system has a total external output power of 4.2MW, equivalent to 42kWh of electricity per ton of LNG. The electricity generated by generator W101 is connected to the receiving station electrical bus for use by the receiving station.

[0055] According to national marine environmental protection requirements, the temperature difference between the inlet and outlet of seawater should be less than 5°C. In the above step 468, the average temperature of the inlet of seawater is 20°C, and the average temperature of the outlet of refrigerant is 15°C.

[0056] The working pressure of my country's LNG receiving stations is high, and the selection of Rankine cycle working medium has a great influence on the power generation efficiency. The present invention selects a mixed refrigerant composed of methane, ethylene and propane, with molar percentages of 32%, 28% and 40% respectively. The working curve of the mixed refrigerant is basically consistent with the gasification curve of LNG, which maximizes the power generation efficiency.

[0057] The main heat exchanger H001 adopts a multi-channel high-pressure plate-fin heat exchanger, which can achieve efficient heat exchange of multiple logistics at the same time. The NG thermostat H201 adopts an open-frame vaporizer commonly used in large LNG receiving stations, and an immersed combustion vaporizer can also be used. Heat exchangers H102, H102, and H103 are used as refrigerant heaters. They can use open-frame vaporizers commonly used in large LNG receiving stations, or industrial waste heat such as hot drainage, waste steam, or an immersed combustion vaporizer as a high-stage heat source to improve the system's power generation and efficiency.

[0058] The Rankine cycle refrigerant booster pump P101 is mainly responsible for refrigerant pressurization and uses a submersible pump. Rankine cycle turbines T101, T102, and T103 use centrifugal turbine expanders. Generator W101 uses a synchronous generator, which is coaxial with Rankine cycle turbines T101, T102, and T103.

[0059] The above-mentioned system using the organic Rankine cycle for efficient cold energy power generation is equipped with a DCS control system during use, which can realize automatic control of the low-temperature organic Rankine cycle according to the LNG export situation and demand, and meet the needs of system intelligent control.

[0060] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and the specific implementation of the present invention cannot be limited to these descriptions. For ordinary technicians in the field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A system for high-efficiency cold energy generation using an organic Rankine cycle, characterized in that: The system comprises a main heat exchanger (H001), a Rankine cycle refrigerant booster pump (P101), an NG thermostat (H201), a heat exchanger No. ① (H101), a heat exchanger No. ② (H102), a heat exchanger No. ③ (H103), a Rankine cycle turbine No. ① (T101), a Rankine cycle turbine No. ② (T102), a Rankine cycle turbine No. ② (T102) and a generator (W101); LNG from a receiving station is connected to a first channel of the main heat exchanger (H001) through a pipeline, the first channel of the main heat exchanger (H001) is connected to the NG thermostat (H201), LNG is gasified into gas in the main heat exchanger, and is temperature-regulated by the thermostat before entering the pipeline network and being transported to users; the Rankine cycle turbine No. ③ (T103) and the second channel of the main heat exchanger (H101) are connected through a pipeline. The second channel of the main heat exchanger (H001) is connected to the refrigerant booster pump (P101) through a refrigerant pipeline, the refrigerant booster pump (P101) is connected to the third channel of the main heat exchanger (H001) through a refrigerant pipeline, the third channel of the main heat exchanger (H001) is connected to the No. ① heat exchanger (H101) through a refrigerant pipeline, the No. ① heat exchanger (H101) is connected to the No. ① turbine (T101) through a refrigerant pipeline, the No. ① turbine (T102) is connected to the No. ② heat exchanger (H102) through a refrigerant pipeline, the No. ② heat exchanger (H203) is connected to the No. ③ turbine (T103) through a refrigerant pipeline, the No. ① turbine (T101), the No. ② turbine (T102) and the No. ③ turbine (T103) work to drive the coaxial generator (W101) to generate electricity.

2. The system for high-efficiency cold energy power generation using an organic Rankine cycle according to claim 1, characterized in that: The main heat exchanger (H001) adopts a multi-channel high-pressure plate-fin heat exchanger, which can realize efficient heat exchange of multiple logistics at the same time; the refrigerant booster pump (P101) adopts a submersible pump.

3. The system for high-efficiency cold energy power generation using an organic Rankine cycle according to claim 1, characterized in that: The heat exchanger No. ① (H101), the heat exchanger No. ② (H102), and the heat exchanger No. ③ (H103) all adopt open-frame vaporizers.

4. The system for high-efficiency cold energy power generation using an organic Rankine cycle according to claim 1, characterized in that: The turbine No. 1 (T101), turbine No. 2 (T102), and turbine No. 3 (T103) all adopt coaxial centrifugal turbine expanders.

5. The system for high-efficiency cold energy power generation using an organic Rankine cycle according to claim 1, characterized in that: The generator (W101) is a synchronous generator, which is coaxial with turbine No. 1 (T101), turbine No. 2 (T102), and turbine No. 3 (T103).

6. The system for high-efficiency cold energy power generation using an organic Rankine cycle according to claim 1, characterized in that: The refrigerant of the power generation system is a mixed working fluid consisting of methane, ethylene and propane.

7. A method for generating electricity using a system for high-efficiency cold energy generation using an organic Rankine cycle as claimed in any one of claims 1 to 6, characterized in that: The steps include: (1) LNG stored at normal pressure and low temperature is pressurized by a high-pressure pump. The pressurized LNG enters the first channel of the main heat exchanger (H001) through a pipeline, and exchanges heat with the gaseous refrigerant in the second channel of the main heat exchanger (H001) in the main heat exchanger (H001). After the heat exchange, the LNG is converted into NG, enters the NG temperature regulator (H201) through a pipeline, and is reheated to above 0°C before entering the pipeline network and being transported to users. (2) The gaseous refrigerant exchanges heat with the LNG in the first channel in the second channel of the main heat exchanger (H001) and condenses into liquid refrigerant; (3) The liquid refrigerant enters the refrigerant booster pump (P101) through the pipeline for pressurization. The liquid refrigerant with increased pressure enters the third channel of the main heat exchanger (H001), exchanges heat with the gaseous refrigerant in the second channel of the main heat exchanger (H001), and a small amount of the refrigerant is vaporized; (4) After completing step (3), the refrigerant enters heat exchanger No. ① (H102) through a pipeline for heat exchange. In this step, the refrigerant is completely vaporized and the temperature rises; (5) The heated gaseous refrigerant enters turbine No. 1 (T101) through a pipeline to perform the first expansion and work. After the work, the temperature of the gaseous refrigerant decreases; (6) After the first expansion, the gaseous refrigerant enters heat exchanger No. ② (H102) through the pipeline for heat exchange and reheating; (7) The reheated gaseous refrigerant enters turbine No. 2 (T102) through a pipeline to expand and perform work for the second time; (8) After the second expansion, the gaseous refrigerant enters heat exchanger No. ③ (H103) through the pipeline for heat exchange and reheating; (9) The reheated gaseous refrigerant enters turbine No. 3 (T103) through a pipeline to expand for the third time to perform work; (10) After the third expansion, the gaseous refrigerant enters the second channel of the main heat exchanger (H001) through the pipeline, forming a refrigerant circulation process; (11) Turbine No. 1 (T101), Turbine No. 2 (T102) and Turbine No. 3 (T102) output power to drive the coaxial generator (W101) to generate electricity, thereby converting LNG cold energy into electrical energy. The electrical energy generated by the generator (W101) can be connected to the electrical bus of the receiving station for use by the receiving station.

8. The power generation method according to claim 7, characterized in that: In step (1), the high-stage heat source may be seawater or an immersed combustion gasifier. In steps (4), (6), and (8), the high-stage heat source may be seawater as the high-temperature stage heat source of the low-temperature Rankine cycle. Industrial waste heat such as hot drainage, waste steam, or an immersed combustion gasifier may be used as the high-stage heat source to improve the power generation efficiency of the system.

9. The power generation method according to claim 7, characterized in that: The pressure of the liquid refrigerant after the pressure increase in step (3) is 22 bar; the pressure of the gaseous refrigerant after the first expansion work is 16 bar; the pressure of the gaseous refrigerant after the second expansion work is 10 bar, and the pressure of the gaseous refrigerant after the third expansion work is 4 bar.

10. The power generation method according to claim 7, characterized in that: The gaseous refrigerant or liquid refrigerant is a mixed working fluid consisting of methane, ethylene and propane, with molar percentages of 32%, 28% and 40% respectively.

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